Field of the Invention
The present invention relates to a display device having touch sensors and a driving method thereof.
Discussion of the Related Art
User interfaces (UI) enable humans (users) to easily control various types of electronic devices as they want. Typical examples of the user interfaces include keypads, keyboards, mice, on-screen displays (OSD), and remote controllers with an infrared communication capability or radio frequency (RF) communication capability. The user interface technology is continuously developing to improve user sensation and ease of operation. Recently, user interfaces have been evolving into touch UI, voice recognition UI, 3D UI, etc.
The touch UI is becoming increasingly indispensable in portable information appliances such as smartphones, and moreover it is being extensively used in laptop computers, computer monitors, home appliances, etc. There has recently been proposed a technology in which touch sensors are embedded in the pixel array of a display panel (hereinafter called “in-cell touch sensor technology”). In the in-cell touch sensor technology, touch sensors can be installed in a display panel without an increase in the thickness of the display panel.
In the in-cell touch sensor technology, electrodes connected to the pixels of the display panel are used as electrodes of the touch sensors. For example, the in-cell touch sensor technology may involve segmenting a common electrode for supplying a common voltage to the pixels of a liquid crystal display and using segmented common electrode patterns as electrodes of the touch sensors.
Since the in-cell touch sensor technology uses segmented common electrode patterns as electrodes of the touch sensors, display noise may be mixed in with a touch sensing signal when the touch sensors are driven while input image data is being written to pixels, which can distort the touch sensing signal.
In order to decrease distortion in the touch sensing signal, in the in-cell touch sensor technology of the related art, one frame period is time-divided into a period (hereinafter, “display interval Td”) for driving the pixels based on a touch synchronization signal Tsync and a period (hereinafter, “touch interval Tt”) for driving the touch sensors, as shown in FIG. 1. In the in-cell touch sensor technology of the related art, the pixels are driven during the display interval Td, and thus, a common voltage Vcom is applied to the common electrode patterns COM, a data signal Vdata corresponding to input image data is applied to data lines D1 and D2, and a gate signal is applied to gate lines G1 and G2. In the in-cell touch technology of the related art, a touch driving signal Tdrv is applied to the common electrode patterns only during the touch interval Tt and reads changes in the amount of electric charge in the touch sensors, thereby preventing display noise from being mixed in with the touch sensing signal.
However, the in-cell touch sensor technology is difficult to secure enough time for sufficient touch and display intervals Tt and Td within one frame period because of time-division driving. This problem gets more severe as resolution and frame frequency increase. If the touch interval Tt is short, touch sensitivity is low since the time allocated for each touch electrode's sensing is short. If the display interval Td is not sufficient, this leads to lack of data charging time for driving the display, thereby deteriorating the picture quality of display images.
In addition, technologies of integrating touch sensors in a display device include add-on type and on-cell type. In the add-on type, a display device and a touch panel are separately manufactured, and then the touch panel is attached to an upper substrate of the display device. In the on-cell type, elements constituting a touch panel are formed directly on the upper surface of a display device. In the on-cell type, especially with an organic light-emitting diode display (OLED), a protective cap for protecting the OLED display is provided on the top, and touch electrodes for a touch panel are formed on the protective cap.
The add-on type and the on-cell type do not lack sufficient touch and display intervals because the touch interval and the display interval are not temporally separated but overlap. However, in a display device having add-on type or on-cell type touch sensors, signal lines for display and the touch sensors form parasitic capacitance, which can attenuate the touch sensing signal and therefore decrease touch sensitivity.